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Community and Q&A

Exterior basement wall insulation – is it worth it?

Dan Moore | Posted in General Questions on

I’ve completed a considerable amount of work to my house over the last couple of years and have made a leaky 1965 house much tighter and well insulated.  One last spot that I have had on my list to improve is a section of basement wall that is about 45′ long in total. There is a walk-out section here so the exposed concrete ranges from full height of the wall (7.5′) around the door to as little as 3′ on the east side of the house. The inside of the basement is finished and is used regularly. When it was finished, rigid foam (r7.5) was used to insulate between wood studs so there is something there, but from what I understand this is below ideal code (Climate Zone 6, Peterborough Ontario) and the thermal bridging of the studs reduces effectiveness of the insulation. Ideally, I would like more insulation here but I am having trouble deciding if I should go to the trouble (the rest of the basement I was able to access from inside and increase to R20 without wood studs so it was continuous). The interior of this section is nicely finished and I don’t feel like ripping it up. The exterior portion is quite accessible, I have access to a mini-excavator and don’t mind taking the job on. My hesitation is due to concerns with ants (we have a decent number of carpenter ants around) and long-term durability of finishing coats. I have seen a number of comments indicating don’t do it if you have carpenter ants and mixed reviews on some of the finishing options mentioned in the article “How to Insulate a Basement Wall” (it was very helpful, thank you).

Should I just forget this exterior foam because of the ants? If I was to do the work, I would likely use a cementitious or acrylic coating to finish. How does this hold up after 5-10 years with lawnmows/kids doing what they do? Any thoughts on if this project is a worthwhile one would be much appreciated.


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  1. Kyle Bentley | | #1

    If accessing the exterior is easy, I would put it there before I ripped up a whole finished basement. This would also give you a good chance to inspect the waterproofing and modernized it if needed. I'll let the others chime in on the carpenter ant situation. It's my understanding that they're more attracted to damp materials, and keeping things dry is an important step to avoiding them.

    1. Dan Moore | | #2

      Good thoughts, thanks. To my knowledge there isn't any waterproofing currently so that in itself could be valuable. We are pretty high and dry, very sandy soils, but during early springs things can get damp.

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